proposed

approved

editing

proposed

Vincenzo Librandi, <a href="/A284716/b284716.txt">Table of n, a(n) for n = 1..200</a>

nonn,more,new

approved

editing

editing

approved

a(n) ~ 4 * 3^(2*n+1/2) / (Pi*n^4). - Vaclav Kotesovec, Apr 02 2017

1, 1, 3, 13, 63, 330, 1838, 10758, 65586, 413639, 2684469, 17852715, 121256457, 838843641, 5897455515, 42058344077, 303787163823, 2219452035639, 16383022072549, 122066094872139, 917245868993865, 6946236553301334, 52979616083094066, 406741647662973594

More terms from Vaclav Kotesovec, Apr 02 2017

Rest[CoefficientList[Series[2*x - 1 + (1-x)^2 * (1 + 5*x - (1-9*x)^(3/4) * (1-x)^(1/4) * HypergeometricPFQ[{-1/4, 3/4}, {1}, 64*x/((x-1)*(1-9*x)^3)])/(6*x^2), {x, 0, 30}], x]] (* Vaclav Kotesovec, Apr 02 2017 *)

approved

editing

editing

approved

qqq

Number of indecomposable permutations avoiding the pattern 2143.

A. L. L. Gao, S. Kitaev, P. B. Zhang. <a href="https://arxiv.org/abs/1605.05490">On pattern avoiding indecomposable permutations</a>, arXiv:1605.05490 [math.CO], 2016.

nonn,more,new

approved

editing

editing

approved